H2 Plant Life and Evolution 



Angiosperms or ordinary flowering plants, is the 

 subject of much controversy. 



Alternation of Generations. The origin of the 

 pteridophytes is a matter of some difference of opin- 

 ion. The weight of evidence in favor of the deriva- 

 tion of the leafy sporophyte of these plants from 

 the sporogonium of some form allied to the existing 

 bryophytes is very strong. The greater elaboration 

 of the sporogonium in such forms as the higher 

 mosses and Anthoceros, with the increasing sub- 

 ordination of the sporogenous function, shows an 

 unmistakable tendency towards the independence of 

 the sporophyte such as is finally reached by the 

 ferns. Between the latter and the mosses are 

 marked similarities in the character of the tissues, 

 e.g., the development of stomata, the green assimi- 

 lative tissue of the assimilative organ of the sporo- 

 phyte, and finally the close correspondence in the 

 details of spore division. These, together with 

 marked similarities in the structure of the gameto- 

 phyte and the reproductive organs, make it exceed- 

 ingly probable that the alternation of generations in 

 the pteridophytes is " antithetic," as it is in the 

 bryophytes ; that is, the sporophyte, or neutral gen- 

 eration, is the result of an elaboration of the strictly 

 terrestrial phase of the plant's life, the lineal de- 

 scendant of the unicellular zygote or resting spore 

 of some green alga, developed by these humble water 

 plants for enduring periods of drought. 



A good many cases of " Apogamy," or the origin 



